The biggest problems thus far that i've seen with most people seem to center around:
* Video Card... this is currently very touchy, because the NVIDIA drivers that ship with the current Kubuntu are old, the NVIDIA 6150 and 6200 cards work best with UI2-AlphaBlending and the 5xxx cards work great with UI2-Masking. Other cards will work in either UI1, or UI2-Masking, you might have to fiddle a bit.... I hope the developers find a solution to allow download/install of the vendor drivers, this would solve so many problems... or at least try to track the latest NVIDIA drivers into deb packages...
* SATA... very strange indeed.. some SATA chips are not supported well with the DVD image, and the CD image seems to have better luck here...
* Network... Make sure you have TWO network cards... one for internal, one for external.. if you have to, DOUBLE NAT.. but run the DHCP and network services.. otherwise you will be fighting tooth and nail for nothing, really.
* Drives... this one heh....This is an example of the two converging worlds of users for this system... Pluto was originally designed as an appliance...drop the drives into the core...go... if you had windows shares, cool! it would find em... if you had a NAS dangling around, it would see it as shares, and just go with the appropriate credentials... I've seen so many users try to force their world view into this setup, at the expense of their own sanity, and I do believe that compromise needs to be done on both the developer and user end of things to make this better.
I hope you'll try again soon, it really is an amazing system. I've been running mine for a while now, and I can't live without it.